Greens push for Senate inquiry into mining tax

LABOR's pain over its under-performing minerals resource rent tax is set to increase when the Greens unveil plans for a wide-ranging inquiry into its design and performance.

The Greens leader, Christine Milne, will open a new line of attack on Labor's left flank, using a lunch-time address to the National Press Club in Canberra on Tuesday to push for a full-scale Senate inquiry.

It would need the backing of the Opposition in the Senate to be successful.

Under the plan, the committee will be tasked with examining all aspects of the MRRT's design and administration including its highly troubled negotiation phase with the big three miners, and ''the extent to which the design of the tax as opposed to other factors such as commodity prices are responsible for the mismatch between actual revenue and revenue projections''.

Also in the Greens' sights are the lack of community consultation; options to strengthen the tax to raise more money from miners; its current impact on the budget; and the extent to which its shortfall has compromised other programs.

The potentially embarrassing election year move will put the minor party on a collision course with the party it backed to form government in the House of Representatives.

It comes as Labor struggles to explain why a super-profits tax that was projected to raise $2 billion in its first year to fund tax breaks for businesses and the low paid - itself a downward revision on previous projections - has turned in just $126 million in its first six months of operation.

Branding Labor as ''too scared'' to take on powerful vested interests, Senator Milne will argue the eventual tax was merely a political fix to silence the miners in the lead-up to the 2010 election.

It is unclear whether the Opposition will back the move but the Greens believe Coalition support is likely, if only to embarrass the government before the election.

The Senate Inquiry is separate from smaller inquiries already under way in the Senate regarding loopholes in the tax which allow big miners to depreciate assets from current market value, and which also allow state governments to increase royalties at the expense of the Commonwealth.

Ms Milne will say she has raised concerns about the mining tax ''in public and in private with the Prime Minister and the Treasurer on numerous occasions''.

''It is now clear that they, like Tony Abbott and Warren Truss are just not prepared to put themselves on the line for the national interest,'' she will say.

''Let us put to rest the nonsense that the mining industry cannot afford to pay more.